In the course of the past few years, the problem of removing heat resulting from the operation of microelectronic devices has elevated from being an important concern to becoming a widely recognized bottleneck limiting further progress of high performance microelectronic devices. Excessive heating affects not only performance, but also reliability. With continuing increase in integration levels and introduction of new 3-D chip and interconnect architectures, the challenge to cool microelectronic devices has become even more difficult.
As an example, traditional single core microprocessors generate a significant amount of heat, which is typically in the range of 20-50 Watts per square centimeter (W/cm2). However, modern multi-core microprocessors result in significantly more heat. Multi-core microprocessors experience a global or uniform heat flux that is typically on the order of 20-50 W/cm2. In addition, multi-core microprocessors experience hot spots resulting from the active cores that are typically in the range of 2 to 10 times greater than the global heat flux (i.e., as much as 500 to 1000 W/cm2). Further compounding the issue, the number of cores that are active at any one time and the specific cores that are active at any one time dynamically changes. As a result of the activation and deactivation of the cores, the hot spots are dynamically moving. The heat issue in multi-core microprocessors is even further compounded by 3-D architectures that utilize stacks of multiple active layers (i.e., multiple layers of active cores).
The traditional approach to remove heat from microelectronic devices is not sufficient to alleviate the dynamically moving hot spots generated in multi-core microprocessors. For example, a traditional heat sink has to target the largest heat flux (i.e., worst case) produced at the hot spots and be able to dissipate such a large flux over the entire semiconductor die on which the microprocessor is formed. Thus, if the multi-core microprocessor is formed on a 1 cm2 die with 10 layers and the worst case hot spot is 1000 W/cm2, then the heat sink would be required to remove 10 kilowatts (kW) of heat (i.e., 1000 W/cm2×10 layers×1 cm2). This is not possible using conventional technology. As such, there is a need for a cooling system for microelectronic devices such as, but not limited to, multi-core microprocessors that have dynamically moving hot spots and, in some cases, multiple active layers.